The ultimate objective of the work to be carried out in the continuation of this project is to better define the role of cytotoxic activated macrophages in resistance to cancer. We plan to better define the in vivo role of macrophages as cytotoxic effector cells by capitalizing on obervations made in earlier work on this project. We found that pretreatment of cytotoxic activated macrophages with trypan blue inhibited their in vitro cytotoxic function. Subsequently, we noted that trypan blue treatment of mice inhibited nonspecific tumor resistance induced by BCG as well as specific tumor resistance. In the proposed work we plan to determine if, in addition to inhibition of macrophage cytoxic function, trypan blue affects other immunologic and nonimmunologic components of host response. The two major questions we wish to anser are: 1) Is trypan blue a selective inhibitor of macrophage cytotoxic function? 2) Is trypan blue the prototype of a group of agents with a unique mechanism of action in the suppression of tissue rejection, e.g., does trypan blue inhibit final cytotoxic effector functions of macrophages but not antigen recognition, T-lymphocyte helper function, or immunologic amplification produced by the proliferation of lymphocytes? Trypan blue as a nontoxic and selective inhibitor could be a useful tool for determining the contribution of cytotoxic activated macrophages in the rejection of normal and neoplastic tissues. To determine if trypan blue is a selective inhibitor of the cytotoxic function of activated macrophages, we plan to perform a number of studies which will assay the effect of trypan blue treatment on immunologic and nonimmunologic reactivity in mice and guinea pigs. Included will be the effect of trypan blue treatment on skin graft rejection, antibody response to sheep red blood cells, nonspecific mitogen-induced lymphocyte stimulation, specific mitogen-induced lymphocyte stimulation, footpad and skin-delayed hypersensitivity responses, MIF production, T-lymphocyte killing of specific target cells, macrophage chemotaxis, as well as other responses related to host defense.